CA1050447A - Brakes - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A brake comprises a pair of arms each pivotally coupled to a base and each carrying a brake block mounted on a brake shoe so that, in use, the brake blocks can engage opposite sides of a brake drum coupled to the apparatus with which the brake is used, spring means biassing the arms about their pivots so that the brake blocks are urged towards one another for effecting braking, and an electro-magnetically-powered brake release mechanism arranged, when energized, to exert a force such as to overcome the spring biassing of the arms and pivot the arms apart so as to release the brake pads from engagement with the drum. The spring means comprises a helical spring mounted under compression between a floating spring seat mounted on one end of a rod pivotally connected at its other end to one of the arms at the end thereof remote from the base, and a fixed spring seat which is mounted on the other brake arm and has a passage through which the rod extends and the brake release mechanism applies its force to the floating spring seat end of the rod. The base and the brake arms are constructed as assemblies of sheet metal pressings, and the electromagnetic parts of the brake release mechanism include lamination stacks which are sandwiched between side plates of one of the arms.

Description

105044'7 BACKC.l~OUND OF TIIE INV~NTION
This in~ention concerns improvements in or relating to brakes and particularly to brakes of a type for cooperation with a brake drum and com- `
prising a pair of arms each pivotally coupled to a ba~e and each carrying a brake block mounted on a ~ -brake shoe so that~ in use~ the brake blocks can engase opposite sides of a brake drum coupled to the apparatus with which the brake is used, spring means biassing the arms about their pivots so that the brake blocks are urged towards one another for effecting braking~ and a powered brake release mecl~nism arranged, when energized, to exert a force such as to over-come the spring biassing of the arms and pivot the arms apart so as to release the brake pads from engage-~ent with the drum. The brake reIease mechanism may be electromagnetically powered ~rom a d.c. source or from an a. c. single or polyphase source for ex- ;
ample, or may be pneum~ically or hydrsulically powered; whilst thi~ in~ention will be described herein with particular reference to electromagneti-cally powered brakes, the invention i~ not restric-ted to such a power source.

STATE~NT O~ PRIOR ART
Brake~ of the above~entioned type ar~ known 25 ~ ~ from the Specification of British Patent 8899?~1 of Dewhurst and Partner Limitcd (to whom the current ~pplication has been assisned) ~nd from the Specification - ~ ., . . :
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~050~47 of British Patent 1 213 642 of Elliston~ Evans and Jackson Limited for example, and have commonly been used for the most arduous and widely varyinS duties such as for example for braking hoists, cranes;
conveyors, machine tools etc., in may kinds of industrial applications.

BRIEF SU~ Y OF TlIE INVENTION

It has been traditional in this art to construct brake mechanisms by employing metal castings for such parts as *he base, the brake arms, the brake shoe~ etc., such castings traditionally providing the rugged strength required for the generally heavy dut~
applications to which the brakes are commonly subjected.
To obtain a sufficient degree of dimensional precision, the traditionally used metal castings required a number of finishing machinings. These.traditional construct-~onal methods produced brakes ~hich have proven satLs-factory in use, but which ~ere heavy and cumbersome and subject to castinS fractures, and, furthermore, thc production and subs'e~uent machining of the cast-inS~ has been a time consuming and costlyj labour intensi~e exercise.
It is an object of this invention to provide a bra~e mechanism which can be constructed without reeourse to traditional and expensive metal casting methods.
A ther object of the invention is to provide , .. . .
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` 1050447 a brake mechanism constructed from pre-formed components which are dimension-ally precise in themselves and require no machining opera~ions to bring them into dimensional tolerance.
A further object of the invention is to provide a brake mechanism of streamline~ and light weight design which nonetheless provides the necessary robust strength for heavy duty applications.
Yet a further object of the invention is to simplify the constructions of brake mechanisms of the type with which the invention is concerned by adopt-ion of a constructional method which provides significant design advantages.
These and further objects of the invention are realized by a brake mechanism construction which takes advantage of constructional methods employ-ing sheet metal pressings or stampings which are dimensionally precise in them-selves and afford further advantages in respect of their light weight ~as compared ~o metal castings) and superior s~rength. The departure from tradi-tional methods taught by the instant invention prorides significant advantages as will become apparent hereinafter.
According to the invention there is provided brake apparatus for braking a brake drum, comprising 8 pair of brake arms each constructed as an assembly of at least one sheer metal pressing, a base formed as an assembly of at least one sheet metal pressing, said arms each being pivotally coupled at one end to said base, a brake block mounted on a brake shoe carriet by each said arm, said brake blocks being arranged for engagement with opposite sides of the brake drum, sait brake shoes being carried by said.brake arms at intermediate locaS-ions thereon, a rod pivotally coupled with the Pnd of one of said brake arms remote from the end thereof which is coupled with said base, a floating spring seat associated with the other of said brake arms and formed to provide a pas-sage therethrough for receiving said rod, said rod extending through said pas-sage, a fixed spring seat at the end of ssid rod spaced from said floating spring seat, a compression spring assembled between said fixed and floating spring seats and around said rod and serv mg to bias said brake arms about ~heir pivots to urge the brake blocks towards one another for effec~ing braking of the drum, and a powered ~ 3 .l .
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brake release mechanism arranged for exerting upon said rod a force to over-come the spring biassing of the arms and to pivot the arms apart, thereby to release the brak~ blocks from the drum.
The particular nature of this invention and the objects and many advantages thereof will be best appreciated from the foilowing detailed description of an electromagnetic brake, adapted to be powered from a single phase a.c. source, which embodies in exemplary fashion all of the features of this invention. The description is made with reference to the accompany-ing drawings.

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~050447 D~SCI~I~TION ()I~ l`ll~ DT~NGS
~igur~-l show~ ~ side elcvation ~iew of the complete brake mechanism;
- Figure 2 shows a top plan view of the brake mech~nism shown in Figure 1;
~igure 3 sho~ an end ele~ation view of the brake mechanism of Figurc~ 1 and 2 viewed from the righ~ hand side;
Figure 4 shows a fragmentary sectional view taken on the line IV-IV in Figure 2;
Figure 5 shows a side elevational view show-ing a magnetic arm and core assembly forming part of the brake mechanism of Figures 1, 2 and 3; ~. .
~i$ure 6 is an elevational ~iew of the assembly of Figure 5 in the direction of the arrow VI
in Figure 5;
Figure 7 is a side elevational view of an armature assembly forming part of the bra~e mechan~sm of Figures 1, 2 and 3; and . Figure 8 is an ele~ational view of the assem-bly of Figure 7 in the direction of the arrow VIII in Figure 7.
DETAILED DESCRIPTION OE THE INnrENTION
Referring first to.Figure 1, the electro-

2~ mag~etic brake sh~wn therein comprlses a base 1 having two angled sections 2 spot-welded thereto so as to pro-vide two spaced paral~el upstands whereto a pair of arm~ 3 and k are piYotall~ connected as shown. Arm 3 will be referred to hereinafter as the '.plain' arm, and arm 4 will be referred to hereinafter as the 'm~gnetic' arm of the brake. Each of the arms 3, 4 carries a pivot-Ally-mounted brake shoe 5,6 respectively wllcrcto ~)5~4~7 a composition brake bloclc 7 is rivetted. Show~ in phantom is a bralce ~rum 8 illustrated in cooperation with the brake mechanism shown in brake-applied con-fi$uration~
The magnetic arm 4 serYes as the principal supporting structure for the brake operatinS mechanisms and, in order to acco~nodate t}liS function, is formed of a pair o~ metal plate.~ of substantial surface area secured together by a number of ri~eted ~~ d struts so as to sandwich between the plates various components of the brake mechanism as described herein-.after. ~he s~ape of the plates forming magnetic arm 4 is shown clearly in Figure 1. The plain arm 3 serves only as a mounting for brake shoe 5 and, whilst formed similarly to the magnetic arm 4, is a considerably smaller structure.
An operatinS linkage 9 couples the upper ends Or the arms 3 and 4 to one another through a compression apring which sarve.s to pro~ide the braking torque of the described bralce mechanism. A push rod 10 is ad-justably secured at one end to the upper end of plain arm 3 by means of a pivotal coupling, and extends across the gap between tne two arms 3, 4 to an upper position on m~gnetic arm 4 where it locates freely within and pa -aes through a coaxial hollow cylindrical bush 11 ~hich i adjustably mounted in a block 12 pi~ote~.~et-ween the two plate~ defining the masnetic arm ~ he push rod 10 terminates beyond the bush ~1 and bl6ck l2 in ~ fixed spring seat 13 which ~erves the functions,

3 firstl~, of definin$ in a~sociation with a correspondins.

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~105()447' floating spring seat 14 on bush 11 a captive location for a double com-pression spring 15, and secondly, of providing a recessed surface 17 to accept application to the push rod 10 of an electromagnetically-generated brake release force. It will be seen that any movement of the push-rod 10 in a direction from left to right as viewed in Figurç 1 will cause the ar~s 3, 4 to pivot apart thereby to release the brake blocks from engagemen~ with the brake drum, : Such brake releasing movement of push rod 10 is achieved by means of an electromagnetically operated brake release mechanism which is designated in Figure 1 generally by the reference numeral 18. The brake release mechanism lB comprises a core assembly 19 and an armature assembly 20. Core assembly 19 is consituted by a generally U-shaped core piece 21 formet of a plurality of correspondingly U-shaped magnetic lami-nations sandwiched between the side plates of magnetic arm 4, and an, energizing winding 22 formed on a rigid plastics material former 23 mount-ed on one limb of the U-shaped core piece Zl. ATma~ure assembly 20 is constituted by a pair of armature side plates rivetted together and sand-wiching therebe~ween a stack 24 of generally I-shaped magnetic laminations formed with slightly projecting pole locations at 25 and 26, and is adap-tcd to bc suspended pivotally from a location 27 between the pla~es compri-sing mag~etic arm 4 as shown. A bridging piece 28 extends between the srmaturo sidc plates and carries a thrust pin 29 the free end of which ~ngages the recessed ond of fixed spring seat 13. A thin plate 16 of non-Dag~etic stainless steel is carried on the thrust pin 29 so as to extend ~nto the air gap between pole face 26 of the armature assembly 20 and the facing upper pcle of the U-shaped laminations 21 constituting the coro assembly 19. This plate 16 cnsures that the air gap is maintained dçspite any slight hammering bac~ of ~he lower pole faccs which might occur with prolonged use.

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l(~S0447' A stop lin-its the extent of cloclcwise pivotal movement ~fforded to arm~ture ~ssembly 20.
The basic opcrating principle of the illus-tr~ted ~rake mechanisn can be appreciated from the afore-- 5 goin~ general description. In the de-ener~ized condition of brake release mechanism 18, the force in compression spring 15 urge~ the push rod 10 in a right-to-left direc-tion thereby pulling the arms 3,4 together so that the brake blocks engage with the brake drum. This condition - ~o is as ~hown in Figure 1. Upon energization of the brake release mechanism, i.e. by driYing energizing winding 22 with an approprlate electric current, armature assembly 20 is pivoted anticlockwise towards core assembly 19, by ~irtue of the magnetic attraction bet-~een the two assem~
blie~, and the thrust pin 29 applies a corresponding ~ovement to the push rod 10 against the action of spring 15 which serves to push the brake arms 3,4 apart thereby to release the brake.
The parts above~described with reference to ~igure 1 will now be considered in fuller detail in order that advantageous constr~'ctional features of the illus-trated brake mechanism might be appreciated. Stated dim~nsions are exemplary for a 150 mm brake and will ~ary depending upon brake size.
The base 1 eo~sists of a 5mm sheet steel press-ing provided with a number Or fixing holes, and the base angle -~ections 2 are each formed of 3mm ~heet steel and are each pro~ided wîth fixins holes for correspondence with the fixins holes in the base 1 and with two bearins holes in the upright portion thereof for accepting the pivotal mountinss of the arms 3 and ~. The two l-ase angle ections 2 are fixed to the base spaced from and ;' ~ . . . _. .

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~L05044~ . -parallel to one another as can be seen clearly from Figures 1 and 3~ and two bearing ~u~hes 30 ~.~ee Figure 3), each Co~.prising a llollolr cylindrical member with reduced end portions, are . welded between the ansle scctions 2 with the reduced end portions received in the bearing holes in the angle section uprishts.
Plain arm 3 consist~ of a pair of 3mm sheet steel pressings 31 and 32 maintained precisely alisned and prec~sely spaced from one another by a palr o~ di~-tance posts 33 havins reduced ends ~hich are rivetedinto receiving holes formed in the pressings 31, 32. A pivot pin boss 34 is _ weldedlto each pressins to accoD~odate a pivot pin 35 providing the pivotal connection of the plain arm 3 to the base 1.
~he pivot pin 35 is retained b~ appropriate circlips.
- A further boss 36 is welded to the i~ner ~ide of each presslng 31, 32 to accommodate a hin~e pin 37 which serves to mount the brake shoe 5 to the plain arm 3. ~inally, the upper e~-of each pressinS 31, 32 is formed ~ith a precise hole serving to receive a respec-tive end of a coupling 38-~Y}liCh serves to secure the right hand end of ~ush rod 10 to-the plain arm 3.
The brake siloes 5 and 6 are identical cne to the other! ~ach comprises a pair of side pieces 39 and a curved frontspiece ~0 all formed as pressinss of 3mm Yheet ~teel. The connected edges of the side ~ieces 39 and the frontspiece 40 ha~e interdisitated castella-tions which are . welded toget}ler to ~rovide ~ robust construction neat in appearance~. Brake ~locks 3 j ~re rlvetted to the frontspiece~ Or the two bralce .. . .
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10504~7 ~hoes. A h.inge pin boss 41 i~ projcction wel~ed to each side piece 39 to receive the hinge pin 37 which securcs the brakc ~hoes 5, 6 to the arms 3, 4 An adjustable friction connection between brake shoes 5, 6 and their supportinS arms 3, 4 is provided by conical sprinss supported by scre~s 42 wllic~
bear against the arms 3, 4 as shown in Figure 3; this ~rictional connection ensures that when the brake is released~ the brake shoes do not pivot downwardly under their o~n weight and trail against the brake drum, but instead maintain their brake-on positions relative to the ~ms 3~
The magnetic arm 4 is constructed similarly to the plain arm 3 but is more .complex in thatlit serves to support the electromagnetic brake release mechanism 18 comprising core assembly 19 and armature assembly 20~ and also provides a mounting for the compression spring 15 and for the actuating end of push rod 10.
The magnetic arm 4 per se consis~s of a pair of 3mm aheet ~teel plates secured together in spaced parallel configuration by three ~b~ded distance posts similar to the posts 33 employed in the construction of plain arm 3. The shape of the plates can be seen most clearly from Figures 5 and 6 where they are referenced ~3 and 44~ Pivot pin bosses 45 and hinge pin bosses 46 and 47 are welded to the plates ~3 and ~4 as shown respect-ively to accommodate a pi~ot pin 48 coupling magnetic arm 4 to base 1, a hinge pin 49 coupling armature assembly 20 to magnetic arm ~ 9 and the hinse pin 37 couplins brake 3o ~hoe 6 to magnetic arm 1~, A cover mountins bracket 50 ~s s~cured to each of the plates ''' ,- , ' :'."' . . ' ' . ' ,," ' . ;, . , . ... _,~

~v ~0so447 43, 44 and serves for n~ountinS a box-like c~ver which provides protection for the electroma~netic componcnts of the brake mechanism.
The core assen~bly 19 of the el~ctromasnetic brake release mechanism 18 is mounted between the si~e plate~ 43, 4~ of ~agnetic arm 4 as sho~ most clearly in Figure 6. The core assembly 1~ comprises a plurality of ~enerally U-shaped lan~inationc 21 which are held in position by the welded-in distance pieces securing plates 43 and l~4 together. As sho~, the ends of the limbs of the stack of U-shaped laminations 21 project beyond the : adjacent parts of the plates 43, ~4 and the faces of the ~ole pieces ' thus defined are $round to a precise flatness. The lo~ermo t of the two 'pole pieces' incor-porates an arrangeme~t for damping the actions of the core and armature a.csemblies; thi~ arrangement has a damper plate 51 secured on each side of the 'pole piece' by means of ri~etted damper p~ns 52, and has slots 53 cut into the face of the 'pole piece' to the depth of the da~per pins 52. The damper arransement provides a cirouit for current flow transverYe to the laminations 21 in the damper plates 51 and the damper pins 52 in re~ponse to chansing flux in the laminations 21 which current flow generate~ R counter ~lux such as to damp the o~ovements of the armature a.q embly 20 relative to the core as~embly 19.
An energi~ing windins 22 (see Fisure 1) wound on ~ rigid plastics material former 23 is n!ounted o~ and around the lower limb of the stack of lalllinations 3 constitutinS the-core a~embly 19.

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armature assembly 20 to be ~ivoted clockwise to clcar coil 22 for replacement. Tlle adju~table stop 75 is comprised by a post 76 screw-threa~edl.y engased with a bar 77, the ~nds of which are lod$ed in ~eceivins slots 78 (see Fi5ure 5~ cut in the side plates 43, 44 of the magnetic arm 4, and abuttins at its lower end aSainst the base plate 1, the effective lensth of the post 76 from the bar 77 to base plate l beins adjust-able by virtue of the ~crew-thre~ded engagement of the post 76 with the bar 77. As will be appreciated, adjust-ment of the effective length of post 76 determines the maximum Couater-clockwise pivotal movement of magnetic arm 4 and therefore determines the maximum brake releas-ing movement which can be applied to arm 4 by the brake release mechanism; suitable adjustment o~ the.effective leng' h of post 76 and of the effective lensth of pu.~h rod lO enables the working movements of the two brake arm~ 3 and ~ to be equalized.
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It will be noticed that the construction of 2~ the brake mechanism herein described takes considerable advantase of sheet steel pressinss. It has been tradi-tional in this art to construct brake mechanisms employ-ing metal castinss for such parts as the base, the arnts, the brake shoe-~ etc. To obtain a sufficient degree of dimensional precision, the castings used of old required n n~nber of finishin~ mac}-inings. The sheet steel presR-~ngs employed in the above-described brake mechanism ~!
are dimension~lly precise in themselves, and afford further advanta~es in respect of their liSht weight (as 3 compared with castings) and ~uperior strength. This ~4 .

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:105~4~7 The armature asscmbl.y 20 is s~own most clearly in ~igures 7 ~nd 8 and can be see~ to comprise two side pi~ces 5~ and 55, formed of 3mm sheet steel~ maintained in ~paced p~rallel relationshi~ by welded distance posts 56 and sandwichins therebetween a stack of lamina~ions 24 formed to proYide pole faces at 25 and 260 A hinse pin boss 57 i~ welded to each side piece 5l~, 55 for - acco~modating the hinge pin 27 (see Figure 1) which couples the armature assembly 20 to the magnetic ar~n ~.
A slot 58 is cut out Or each side piece 54, 55 and serves in the assembled brake mechanism to accommodate the bridging piece 28 (see Figure 1) which carries the thrust pin 29 acting on the end of fixed spring seat 13. As sho-~ in Figure 2, and extension of the bridging piece 28 is rigidly coupled with a member 59 which is journalled on pivot pin 49 and projects through the cover of the mechanism to provide a facility for manual release of the brake. ~
The details of the operating linkage 9 and its cooperation with the compression spring 15 and armature acsembly 20 will now be described with particular refer- -ence to Fisures 1, 2 and ~. Push rod lQ is a steel rod . - the right-hand end of which (as viewed in ~igure 1) has a screw threaded portion which passes freely through a diametric bore formed in the coupling 38. Locking nuts 60 serve to adjustably secure the end of push rod 10 relative to coupling 38. The rod 10 extends free~ly through an axial bore formed in brass bush 11 which is "
in turn screw-threadedly, and *hereby adjustably, secured - in a ~teel block 12 pivotally mounted on stub sha~ts 61 .
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1050~4~7 engaged in receivinS holes in the side plates ~3, 44 of maSnetic arm 4. Bras~ bush 11 is formed ~ith a hexagonal end 62 whereby the position of the bush 11 in block 12 can be adjusted~ a locking nut 63 beins provide(l to lock the bush 11 in the block 12, and at the other end provides an a~u~lent for the floating spring seat 14.
Rod 10 passes completely through the bush 11 and ends, on the left-hand side of Figure 1~ in the fixed spring ~eat 13. The space between the fixed spring seat 13 and the floating spring seat 14 abutting bush 11 serves as a capture location for compression spring 15 which is formed as a double helical spring. The adjustment of the bush 11 in the block 12 se^rve~ to set the compression of ~pring 15 and thereby determines the brake torque of the ~ 15 brake mechanism. The adjustment afforded at the screw-threaded end portion of push rod 10 enables the workins clearances of the brake blocks 7 from the brake drum 8 to be adjusted throush adjustment of the effective lensth of push rod lOo ' .
Other de~ails of the illustrated bral~e mechanis~
which have not previously been nlentioned herein are the - back stop 70 (see Figure 1) provided to limit the extent Or clockwise pivotal movement Or armatu~e assembly 20, and the adjustable stop 75 (see Fisure 1) provide~ to e~able the workins movem0nt of the two brake shoes to be balanced. The bacl~ stop 70 com~rise~ a pin 71 releas-ably located in holes provided in t~o metal brackets 72 q secured to the side plates 43 and 4~l of ma~rletic arm 4;
the~e s~me brackets provide fixin~ points for th~ lid 3 of the box-like casinS~ ~elease of t~le pin 71 enal~les ,: : ` .
, - :~0504~7 dep~rture from traditional construction n~ethods pro-vides ~ignificant advantag~s, for exalnple witness tl1e simplicity of construction of the electrom~gnetic brake release mechanism, wherein thc magnetic laminations are conveniently sandwic}led between structural sheet met~l , pressinss, and the simplicity of the br~e shocs.
The siting of the compression spring 15 also represents a notable feature of the described brake ~echanism. It has been known to have the sprinS l~cated adjacent the base bet~Yeen the lower ends of the plain and masnetic arms, with the spring acting on extensions of the arms do-mwards beyond their pivotal connections to the baso. The positioning Or the spring in tlle upper position shown has a nwnber of advantages. ~'irstly, it enables the height of the brake mechanism to be reduced by obviatins the need for the just-mentioned arm exten-sions which enables the pivotal connections Or the ~rms to the base to be made closer to t~e base. Secondly, it enables a more efficient arransement of the spring to be realised as compare~ Wi~il the just-mentioned 1ino~m arransement ~Yherein the brake torque developed at the brake blocks by the ~prinS wa-q subject to the mechanical d~sadvantage occa~ioned by the sprinS force actinS on a short lever (the aboYe-mentioned arm extensions) to develop a brake torque applied over a relatively long le~er ti.e. the arms them~elves); inter alia, tilis enables a less powerful li~hter duty spring to be used to develop the same brake torque which si~plifi~s the housin~ and servicing of the ~4pring-A ~urther ~isnificant advantage can obtain from .

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10504~
the clean arr~n~ement of the plain arm which9 on relcas-ing the push rod 10 from the coupling 38, enables the plain arm to be laid flat. This facility can be advant~geous in regard to tl-e fittins of the brake to an existinS installation ~here there is minimum clearance beneath the brake drum. I~hereas hitherto it may have been nesessary to dismantle the plain arm completely from the brake mecha~ism for fitting the brake mechanism into an existing installation, the present arrangement might merely require the plain arm to be pivoted flat with the base. Il It will be noted furthermore that the opening of the connection between the push rod anl the plain arm for installation of the brake mechanism does not interfere ~ J
with the brake torque setting.
The arrangement of the compression spring 15 is designed for facilitating spring force adjustment for setting the brake torqua, the adjustment of the bush 11 in the block 12 providing this adjustment. The bral;e torque can be precise~ set and, by ~irtue of the limited range of adjustment afforded to bush 11 in block 12, it can be made impossible to over-torque the brake mechanism.

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Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Brake apparatus for braking a brake drum, comprising a pair of brake arms each constructed as an assembly of at least one sheet metal pres-sing, a base formed as an assembly of at least one sheet metal pressing, said arms each being pivotally coupled at one end to said base, a brake block mounted on a brake shoe carried by each said arm, said brake blocks being arranged for engagement with opposite sides of the brake drum, said brake shoes being carried by said brake arms at intermediate locations thereon, a rod pivotally coupled with the end of one of said brake arms remote from the end thereof which is coupled with said base, a floating spring seat associated with the other of said brake arms and formed to provide a passage therethrough for receiving said rod, said rod extending through said passage, a fixed spring seat at the end of said rod spaced from said floating spring seat, a compression spring assembled between said fixed and floating spring seats and around said rod and serving to bias said brake arms about their pivots to urge the brake blocks towards one another for effecting braking of the drum, and a powered brake release mechanism arranged for exerting upon said rod a force to over-come the spring biassing of the arms and to pivot the arms apart, thereby to release the brake blocks from the drum.

2. Brake apparatus for braking a brake drum, comprising a pair of brake arms each constructed as an assembly of at least one sheet metal pressing, a base formed as an assembly of at least one sheet metal pressing, said arms each being pivotally coupled at one end to said base, a brake block mounted on a brake shoe carried by each said arm, said brake blocks being arranged for engagement with opposite sides of the brake drum, said brake shoes being carried by said brake arms at intermediate locations thereon, a rod pivotally coupled with the end of one of said brake arms remote from the end thereof which is coupled with said base, a floating spring seat associated with the other of said brake arms and formed to provide a passage therethrough for receiving said rod, said rod extending through said passage, a fixed spring seat at the end of said rod spaced from said floating spring seat, a compres-sion spring assembled between said fixed and floating spring seats and around said rod and serving to bias said brake arms about their pivots to urge the brake blocks towards one another for effecting braking of the drum, and a powered brake release mechanism arranged for exerting upon said rod a force to overcome the spring biassing of the arms and to pivot the arms apart, thereby to release the brake blocks from the drum, said powered brake release mechanism comprising an electromagnetic arrangement having an armature part and a coil part, one of said parts being pivotally mounted on the said other of the brake arms and the other of said parts being fixedly mounted thereon, ant means being provided to transmit relative movement of the parts, responsive to energization of said coil, to said rod.

3. A brake as claimed in claim 2, wherein said armature part of the electromagnetic arrangement is pivotally mounted on the said other of the brake arms and said coil part is fixedly mounted thereon.

4. A brake as claimed in claim 1 wherein said powered brake release mechanism comprises an electromagnetic arrangement having an armature assembly and a coil assembly, the said armature assembly being pivotally mounted on the said other of the brake arms and the said coil assembly being fixedly mounted thereon, and means being provided to transmit a brake releasing movement of the armature, responsive to energization of said coil, to said rod.

5. A brake as claimed in claim 4 wherein said coil assembly of the electromagnetic arrangement comprises a core assembly constituted by a stack of laminations, and the said laminations are sandwiched between a pair of sheet metal pressings which are pivotally mounted on the said other of the brake arms.

6. A brake as claimed in claim 5 wherein said laminations are generally U-shaped, and said coil assembly of the electromagnetic arrangement includes an energizing winding mounted on and around one limb of the lamination stack.

7. A brake as claimed in claim 6 wherein said armature assembly is arranged generally to bridge the ends of the U-shaped laminations, and com-prises a stack of laminations sandwiched between a pair of sheet metal side pieces having extensions providing a pivotal mounting for the armature assembly.

8. A brake as claimed in claim 4 wherein said armature assembly includes a thrust pin in abutting relationship with the end of said rod, the end of said thrust pin being received in an indentation formed for the pur-pose in the head of the floating spring seat.

9. A brake as claimed in claim 1 wherein said fixed spring seat is adjustable relative to the said other brake arm whereby the compression of said spring may be adjusted.

10. A brake as claimed in claim 1 including an adjustable stop associ-ated with one of the brake arms to determine the maximum extent of pivotal movement thereof away from the other brake arm.